1. Field of the Invention
The present invention relates to a head positioning control system, for use in a disk drive, for situating a head in a target position, and more particularly to a servo system for executing track following control to position the head on a predetermined portion of a target track of a disk.
2. Description of the Related Art
A disk drive represented by a hard disk drive employs a servo system for situating a head in a target position (on a track to be accessed) on a disk as a data recording medium. The servo system uses servo data read by the head from a servo area provided on the disk so as to control an actuator (i.e. a plant) that mounts the head thereon. The servo system executes a seek operation for moving the head to a target track by controlling the actuator, and a track following operation for positioning the head on a predetermined portion of a target track. In this description, the system that executes the track following operation is called a “head positioning control system”.
In light of the above, a head positioning control system is now proposed, in which the position error following performance is improved when a target value fluctuates at a characteristic frequency. The system is disclosed in U.S. patent application Ser. No. 09/389,367 and Japanese Patent Application KOKAI Publication No. 2000-195202.